With the advance of precision technology the size of electronic devices such as personal computers shrinks gradually but performance increases constantly. Heat dissipating of the electronic devices become a serious problem. R.O.C. patent publication No. 200619900 discloses a temperature sensitive radiator that has a temperature detection circuit containing a thermal sensitive resistor or other temperature sensitive elements to constantly detect temperature alterations of the heat source of an electronic device during operation. In the event that the temperature of the heat source exceeds a preset temperature level a signal is issued to a driving circuit to increase the rotation speed of the radiator to increase the heat dissipating effect.
However the approach mentioned above can no longer meet the requirements of the present electronic devices. For instance a generally personal computer has many heat sources, such as power supply, CPU, hard disk drives, display cards and chassis and the like. A plurality of air fans have to be installed corresponding to the heat sources to reduce the temperature thereof. In the conventional air fan control architecture when a higher temperature of one heat source is detected the rotation speed of one air fan is regulated through the driving power. But temperature increase of one heat source often causes a higher temperature in the entire system environment due to thermal convection. The conventional air fan design does not take into account of the adverse effect caused by the accumulating heat of the environment. Each air fan is responsible for heat dissipating of a single heat source. The rotation speeds of the air fans in the system are not controlled integrally (for instance the rotation speed of the air fan for the chassis also has to be increased to dissipate the heated air outside the chassis). As a result, thermal convection tends to make the temperature of the entire system higher and total heat dissipating efficiency is affected. The problem of the accumulating heat in the environment remains unresolved.